Semiconductor device and method for manufacturing the same

ABSTRACT

A semiconductor device and a method of manufacturing a semiconductor device are provided. The semiconductor device includes a substrate having a trench and a gate structure in the trench. The trench includes a lower gate electrode, an upper gate electrode over the lower gate electrode and a first dielectric layer partially disposed between the lower gate electrode and the upper gate electrode.

TECHNICAL FIELD

The present disclosure relates to a semiconductor device and a method for manufacturing a semiconductor device, and more particularly, to a buried gate structure having a dielectric layer between two electrodes.

DISCUSSION OF THE BACKGROUND

A buried gate structure of a semiconductor device includes a gate dielectric layer and a gate electrode in a trench. The gate dielectric layer covers the surface of the trench and the gate electrode partially fills the trench on the gate dielectric layer. The buried gate structure may be adjacent to (or on the same level as) impurity regions or junction regions in an active region of the semiconductor device.

Gate induced drain leakage (GIDL) may increase where the gate electrode and the impurity regions overlap. GIDL discharges the stored charges, thereby deteriorating the operational reliability of the semiconductor device. Moreover, a portion of a buried gate structure of the semiconductor device may be disposed in an isolation region of the semiconductor device, which is referred to as a passing gate. The passing gate may exacerbate the occurrence of GIDL.

This Discussion of the Background section is provided for background information only. The statements in this Discussion of the Background are not an admission that the subject matter disclosed herein constitutes prior art with respect to the present disclosure, and no part of this Discussion of the Background may be used as an admission that any part of this application constitutes prior art with respect to the present disclosure.

SUMMARY

One aspect of the present disclosure provides a semiconductor device. The semiconductor device includes a substrate having a trench and a gate structure in the trench. The gate structure includes a lower gate electrode, an upper gate electrode over the lower gate electrode and a first dielectric layer partially disposed between the lower gate electrode and the upper gate electrode.

Another aspect of the present disclosure provides a semiconductor device. The semiconductor device includes a substrate having a trench and a gate structure in the trench. The gate structure includes a lower gate electrode and an upper gate electrode over the lower gate electrode. The lower gate electrode and the upper gate electrode are configured to receive different voltages.

Another aspect of the present disclosure provides a method of manufacturing a semiconductor device. The method includes forming a trench in a substrate, disposing a lower gate electrode in the trench, and disposing a first dielectric layer on the lower gate electrode. The method also includes disposing an upper gate electrode on the first dielectric layer.

In some embodiments, the method further comprises disposing a second dielectric layer in the trench, wherein the lower gate electrode is spaced apart from the substrate by the second dielectric layer.

In some embodiments, the second dielectric layer is disposed by a thermal oxidation process.

In some embodiments, the first dielectric layer is disposed by an atomic layer deposition (ALD) process.

In some embodiments, the method further comprises disposing a first barrier layer in the trench, wherein the lower gate electrode is spaced apart from the substrate by the first barrier layer.

In some embodiments, the first dielectric layer is disposed on the first barrier layer.

In some embodiments, the method further comprises partially removing the first barrier layer to expose a part of the second dielectric layer.

In some embodiments, the first dielectric layer is disposed on the part of the second dielectric layer.

In some embodiments, the method further comprises disposing a second barrier layer on the first dielectric layer.

Forming a thicker dielectric layer between the upper electrode and the substrate may reduce the effective electric field and consequently reduce GIDL. Therefore, interference between word-lines in different memory cells can be avoided. A data retention time can be extended, and the operational reliability of the semiconductor device can also be improved.

In addition, the lower gate electrode and the upper gate electrode can receive different voltages, which helps to mitigate GIDL while maintaining good device performance.

The foregoing has outlined rather broadly the features and technical advantages of the present disclosure so that the detailed description of the disclosure that follows may be better understood. Additional features and advantages of the disclosure will be described hereinafter, and form the subject of the claims of the disclosure. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures or processes for carrying out the same purposes of the present disclosure. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the disclosure as set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present disclosure may be derived by referring to the detailed description and claims when considered in connection with the Figures, where like reference numbers refer to similar elements throughout the Figures, and:

FIG. 1A is a schematic plane view of a semiconductor device in accordance with some embodiments of the present disclosure.

FIG. 1B is a schematic cross-sectional view illustrating the semiconductor device taken along an A-A′ line shown in FIG. 1A.

FIG. 1C is a schematic cross-sectional view illustrating the semiconductor device taken along a B-B′ line shown in FIG. 1A.

FIG. 2 is a schematic cross-sectional view of a semiconductor device in accordance with some embodiments of the present disclosure.

FIG. 3 is a schematic cross-sectional view of a semiconductor device in accordance with some embodiments of the present disclosure.

FIG. 4A illustrates one or more stages of a method of manufacturing a semiconductor device in accordance with some embodiments of the present disclosure.

FIG. 4B illustrates one or more stages of a method of manufacturing a semiconductor device in accordance with some embodiments of the present disclosure.

FIG. 4C illustrates one or more stages of a method of manufacturing a semiconductor device in accordance with some embodiments of the present disclosure.

FIG. 4D illustrates one or more stages of a method of manufacturing a semiconductor device in accordance with some embodiments of the present disclosure.

FIG. 4E illustrates one or more stages of a method of manufacturing a semiconductor device in accordance with some embodiments of the present disclosure.

FIG. 4F illustrates one or more stages of a method of manufacturing a semiconductor device in accordance with some embodiments of the present disclosure.

FIG. 4G illustrates one or more stages of a method of manufacturing a semiconductor device in accordance with some embodiments of the present disclosure.

FIG. 4H illustrates one or more stages of a method of manufacturing a semiconductor device in accordance with some embodiments of the present disclosure.

FIG. 4I illustrates one or more stages of a method of manufacturing a semiconductor device in accordance with some embodiments of the present disclosure.

FIG. 4J illustrates one or more stages of a method of manufacturing a semiconductor device in accordance with some embodiments of the present disclosure.

FIG. 4K illustrates one or more stages of a method of manufacturing a semiconductor device in accordance with some embodiments of the present disclosure.

FIG. 4L illustrates one or more stages of a method of manufacturing a semiconductor device in accordance with some embodiments of the present disclosure.

FIG. 4M illustrates one or more stages of a method of manufacturing a semiconductor device in accordance with some embodiments of the present disclosure.

FIG. 4N illustrates one or more stages of a method of manufacturing a semiconductor device in accordance with some embodiments of the present disclosure.

FIG. 4O illustrates one or more stages of a method of manufacturing a semiconductor device in accordance with some embodiments of the present disclosure.

FIG. 5 illustrates a flow chart of a method of manufacturing a semiconductor device in accordance with some embodiments of the present disclosure.

DETAILED DESCRIPTION

Embodiments, or examples, of the disclosure illustrated in the drawings are now described using specific language. It shall be understood that no limitation of the scope of the disclosure is hereby intended. Any alteration or modification of the described embodiments, and any further applications of principles described in this document, are to be considered as normally occurring to one of ordinary skill in the art to which the disclosure relates. Reference numerals may be repeated throughout the embodiments, but this does not necessarily mean that feature(s) of one embodiment apply to another embodiment, even if they share the same reference numeral.

It shall be understood that, although the terms first, second, third, etc., may be used herein to describe various elements, components, regions, layers or sections, these elements, components, regions, layers or sections are not limited by these terms. Rather, these terms are merely used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present inventive concept.

The terminology used herein is for the purpose of describing particular example embodiments only, and is not intended to be limited to the present inventive concept. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It shall be further understood that the terms “comprises” and “comprising,” when used in this specification, point out the presence of stated features, integers, steps, operations, elements, or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or groups thereof.

FIG. 1A is a schematic plane view of a semiconductor device 1 in accordance with some embodiments of the present disclosure. FIG. 1B is a schematic cross-sectional view illustrating the semiconductor device 1 taken along an A-A′ line shown in FIG. 1A. FIG. 1C is a schematic cross-sectional view illustrating the semiconductor device 1 taken along a B-B′ line shown in FIG. 1A.

In some embodiments, the semiconductor device 1 may be disposed adjacent to a circuit. For example, the semiconductor device 1 may be disposed adjacent to a memory device such as a dynamic random access memory (DRAM) device or the like.

Referring to FIG. 1A, the semiconductor device 1 may include a plurality of active regions 10 a and an isolation region 10 i (or an isolation layer) formed on a substrate 10. The active regions 10 a may be defined by the isolation region 10 i.

The semiconductor device 1 may also include a plurality of gate structures, such as the gate structures 11, 12, 13 and 14. Each active region 10 a may cross two gate structures and may be divided into three doped regions by the two gate structures. For example, the active region 10 a may be divided into the first doped region 101 disposed between the two gate structures 12 and 13 and second doped regions 102 located at two sides of the first doped region 101.

The gate structures 11, 12, 13 and 14 may each have a line shape extending in any one direction. The gate structures 11, 12, 13 and 14 may each be a buried gate buried in a trench that runs through the active regions 10 a and the isolation region 10 i. The gate structures 11, 12, 13 and 14 may each include one or more main gate parts (or main gates) buried in the active regions 10 a and one or more passing gate parts (or passing gates) buried in the isolation region 10 i. For example, FIG. 1B shows a passing gate of the gate structure 11, a main gate of the gate structure 12, a main gate of the gate structure 13 and a passing gate of the gate structure 14. FIG. 1C shows a trench 10 t 2 (where the gate structure 12 is disposed) that runs through one of the active regions 10 a and the isolation region 10 i. The portion of the gate structure 12 over the active region 10 a is a main gate.

As used herein, the term “main gate” refers to a gate that is configured to receive a voltage to address a memory cell, and the term “passing gate” refers to a gate that is configured to receive a voltage to address an adjacent memory cell.

For example, the gate structure 11 may be a passing gate in one memory cell shown in FIG. 1B, but becomes a main gate in another memory cell. In some embodiments, the gate structure 12 may be a main gate in one memory cell shown in FIG. 1B, but becomes a passing gate in yet another memory cell.

Although the main gate and the passing gate are both described above as being parts or portions of the gate structure, the main gate and the passing gate have different structures. For example, as shown in FIG. 1B, the trench 10 t 1 for the passing gate part of the gate structure 11 and the trench 10 t 2 for the main gate part of the gate structure 12 have different depths. The trench 10 t 1 may be deeper than the trench 10 t 2.

Referring to FIG. 1B, the semiconductor device 1 may include the substrate 10, and the gate structures 11, 12, 13 and 14 formed in the substrate 10.

The substrate 10 may include a semiconductor substrate. In some embodiments, the substrate 10 may include, for example, silicon (Si), monocrystalline silicon, polysilicon, amorphous silicon, germanium (Ge), silicon germanium (SiGe), silicon carbide (SiC), silicon germanium carbide (SiGeC), gallium (Ga), gallium arsenide (GaAs), indium (In), indium arsenide (InAs), indium phosphide (InP) or other IV-IV, III-V or II-VI semiconductor materials. In some other embodiments, the substrate 10 may include a layered semiconductor such as silicon/silicon germanium, silicon-on-insulator, or silicon germanium-on-insulator.

The active region 10 a and the isolation region 10 i may be formed in the substrate 10. The active region 10 a may be defined by the isolation region 10 i. In some embodiments, the isolation region 10 i may include shallow trench isolation (STI) structures. The STI structures may include, for example, silicon oxide (SiO₂), silicon nitride (Si₃N₄), silicon oxynitride (N₂OSi₂), silicon nitride oxide (N₂OSi₂), etc.

The first doped region 101 and the second doped regions 102 may be formed in the active region 10 a. In some embodiments, the first doped region 101 and the second doped regions 102 may be disposed over or proximal to the top surface of the active region 10 a. The first doped region 101 and the second doped region 102 may be located on both sides of the trench 10 t 2.

In some embodiments, the first doped region 101 and the second doped region 102 may be doped with an N-type dopant such as phosphorus (P), arsenic (As), or antimony (Sb). In some other embodiments, the first doped region 101 and the second doped region 102 may be doped with a P-type dopant such as boron (B) or indium (In). In some embodiments, the first doped region 101 and the second doped region 102 may be doped with dopants or impurity ions having the same conductivity types. In some embodiments, the first doped region 101 and the second doped region 102 may be doped with dopants or impurity ions having different conductivity types.

The bottom surfaces of the first doped region 101 and the second doped region 102 may be located at a predetermined depth from the top surface of the active region 10 a. The first doped region 101 and the second doped region 102 may contact sidewalls of the trench 10 t 2. The bottom surfaces of the first doped region 101 and the second doped region 102 may be higher than the bottom surface of the trench 10 t 2. Similarly, the bottom surfaces of the first doped region 101 and the second doped region 102 may be higher than the bottom surface of the trench 10 t 1.

In some embodiments, the first doped region 101 and the second doped region 102 may be referred to as source/drain regions. In some embodiments, the first doped region 101 may include a bit-line contact region and may be electrically connected with a bit-line structure (such as the bit-line structure 32 shown in FIG. 3 ). The second doped region 102 may include a storage node junction region and may be electrically connected with a memory element (such as the memory element 34 shown in FIG. 3 ).

The trench 10 t 1 in the isolation region 10 i and the trench 10 t 2 in the active region 10 a are spaces in which the gate structures 11 and 12 may be formed. The gate structure 11 in the isolation region 10 i may include a passing gate. The gate structure 12 in the active region 10 a may include a main gate.

The trench 10 t 2 may have a shallower depth than the trench 10 t 1. The bottom of the trenches 10 t 1 and 10 t 2 may each have a curvature as shown in the embodiment of FIG. 1B. However, in some other embodiments, the bottom of the trenches 10 t 1 and 10 t 2 may be flat or may have other shapes.

The gate structure 12 may include dielectric layers 12 d 1, 12 d 2, gate electrodes 12 e 1, 12 e 2, and a capping layer 12 c.

The dielectric layer 12 d 1 may be conformally formed on the bottom surface and sidewall of the trench 10 t 2. The dielectric layer 12 d 1 may surround or cover a part of the gate electrode 12 e 1. The dielectric layer 12 d 1 may separate the gate electrode 12 e 1 from the substrate 10.

A part of the dielectric layer 12 d 1 may be disposed between the gate electrode 12 e 1 and the substrate 10. A part of the dielectric layer 12 d 1 may be disposed between the gate electrode 12 e 2 and the substrate 10.

In some embodiments, the dielectric layer 12 d 1 may include, for example, silicon oxide (SiO₂), silicon nitride (Si 3 N₄), silicon oxynitride (N₂OSi₂), silicon nitride oxide (N₂OSi₂), a high-k material or combinations thereof. Examples of the high-k material include a dielectric material having a dielectric constant that is higher than that of silicon dioxide (SiO₂), or a dielectric material having a dielectric constant higher than about 3.9. In some embodiments, the dielectric layer 12 d 1 may include at least one metallic element, such as hafnium oxide (HfO₂), silicon doped hafnium oxide (HSO), lanthanum oxide (La₂O₃), lanthanum aluminum oxide (LaAlO₃), zirconium oxide (ZrO₂), zirconium orthosilicate (ZrSiO₄), aluminum oxide (Al₂O₃) or combinations thereof.

The dielectric layer 12 d 2 may be disposed on the gate electrode 12 e 1. The dielectric layer 12 d 2 may be partially disposed between the gate electrodes 12 e 1 and 12 e 2. For example, the dielectric layer 12 d 2 may have a base portion between the gate electrodes 12 e 1 and 12 e 2 and an extending portion extending from the base portion to the top surface of the active region 10 a.

The base portion of the dielectric layer 12 d 2 may directly contact the gate electrodes 12 e 1 and 12 e 2. The base portion of the dielectric layer 12 d 2 may be sandwiched between the gate electrodes 12 e 1 and 12 e 2. The base portion of the dielectric layer 12 d 2 may be covered or embedded by the gate electrodes 12 e 1 and 12 e 2.

The extending portion of the dielectric layer 12 d 2 may cover or contact a part of the dielectric layer 12 d 1. The extending portion of the dielectric layer 12 d 2 may be disposed between the gate electrode 12 e 2 and the dielectric layer 12 d 1 and between the capping layer 12 c and the dielectric layer 12 d 1. The extending portion of the dielectric layer 12 d 2 may be spaced apart from the substrate 10 by the dielectric layer 12 d 1.

The dielectric layer 12 d 2 may surround or cover a part of the gate electrode 12 e 2. The dielectric layer 12 d 1 and the extending portion of the dielectric layer 12 d 2 may separate the gate electrode 12 e 2 from the substrate 10. Therefore, the distance t2 between the gate electrode 12 e 2 and the substrate 10 may be greater than the distance t1 between the gate electrode 12 e 1 and the substrate 10. For example, the gate electrode 12 e 2 and the gate electrode 12 e 1 may be spaced apart from the substrate 10 by different distances.

Any two of a surface of the dielectric layer 12 d 1, a surface of the extending portion of the dielectric layer 12 d 2, a surface of capping layer 12 c, and the top surface of the active region 10 a may be substantially coplanar.

The material that the dielectric layer 12 d 2 is made of may be the same as or different from that of the dielectric layer 12 d 1. In some embodiments, the dielectric layer 12 d 2 and the dielectric layer 12 d 1 may have the same material formed by different operations.

For example, the dielectric layer 12 d 1 may be formed by a thermal oxidation operation. The dielectric layer 12 d 2 may be formed by an atomic layer deposition (ALD) process.

In some embodiments, the dielectric layer 12 d 1 and the dielectric layer 12 d 2 may have different densities, such as different particle densities. For example, a density of the dielectric layer 12 d 1 may be lower than a density of the dielectric layer 12 d 2. A density of the dielectric layer 12 d 2 may be higher than a density of the dielectric layer 11 d 1. For example, the dielectric layer 12 d 2 may be denser than the dielectric layer 12 d 1.

The gate electrode 12 e 1 may be disposed on the dielectric layer 12 d 1 and spaced apart from the substrate 10 by the dielectric layer 12 d 1. The gate electrode 12 e 1 may be spaced apart from the substrate 10 by the distance t1.

The gate electrode 12 e 1 may be surrounded or covered by the dielectric layer 12 d 1 and the dielectric layer 12 d 2. The gate electrode 12 e 1 may also be referred to as a lower gate electrode with respect to the gate electrode 12 e 2.

In some embodiments, the gate electrode 12 e 1 may include a single layer of metal, metal composite or layers of conductive materials. In some embodiments, the gate electrode 12 e 1 may include a metal-based material. For example, the gate electrode 12 e 1 may include titanium (Ti), titanium nitride (TiN), tantalum (Ta), tantalum nitride (TaN), tungsten (W), tungsten nitride (WN), a stack thereof or a combination thereof.

The gate electrode 12 e 2 may be disposed on the dielectric layer 12 d 2 and spaced apart from the gate electrode 12 e 1 by the dielectric layer 12 d 2. The gate electrode 12 e 2 may be spaced apart from the substrate 10 by the dielectric layer 12 d 1 and the dielectric layer 12 d 2. The gate electrode 12 e 2 may be spaced apart from the substrate 10 by the distance t2.

The gate electrode 12 e 2 may be spaced apart from the second doped region 102 by the distance t2. The gate electrode 12 e 2 may be spaced apart from the first doped region 101 by the distance t2.

The gate electrode 12 e 2 may be surrounded or covered by the dielectric layer 12 d 2 and the capping layer 12 c. The gate electrode 12 e 2 may also be referred to as an upper gate electrode with respect to the gate electrode 12 e 1.

In some embodiments, the gate electrode 12 e 2 may include a single layer of metal, metal composite or layers of conductive materials. In some embodiments, the gate electrode 12 e 2 may include polycrystalline silicon (poly-Si), titanium nitride (TiN), tungsten nitride (WN), or the like.

In some embodiments, the gate electrodes 12 e 1 and 12 e 2 may function as word-lines. For example, the gate electrodes 12 e 1 and 12 e 2 may be used with bit-lines (such as the bit-line structure 32 shown in FIG. 3 ) to address memory cells. For example, the gate electrode 12 e 2 may function as a gate electrode of a transistor in a memory cell. The second doped region 102 and the first doped region 101 may function as a drain region and a source region of the transistor. The second doped region 102 may be coupled to a capacitor or a memory element (such as the memory element 34 shown in FIG. 3 ) and the first doped region 101 may be coupled to a bit-line (such as the bit-line structure 32 shown in FIG. 3 ). The transistor may retain charge in the capacitor.

In some embodiments, the gate electrode 12 e 2 may have a low work function. In some embodiments, the gate electrode 12 e 1 may have a high work function. The high work function refers to a work function higher than a mid-gap work function of silicon. A low work function refers to a work function lower than the mid-gap work function of silicon. Specifically, the high work function may be higher than 4.5 eV, and the low work function may be lower than 4.5 eV.

In some embodiments, the gate electrodes 12 e 1 and 12 e 2 may be configured to receive different voltages. In some embodiments, a voltage applied on the gate electrode 12 e 1 may be greater than a voltage applied on the gate electrode 12 e 2. In some embodiments, a voltage difference between the gate electrodes 12 e 1 and 12 e 2 may be greater than 0.3 volts (V). In some embodiments, the gate electrodes 12 e 1 and 12 e 2 may be configured to address different memory cells.

The capping layer 12 c may be disposed on the gate electrode 12 e 2. The capping layer 12 c may contact the extending portion of the dielectric layer 12 d 2. The capping layer 12 c may be spaced apart from the dielectric layer 12 d 1 by the dielectric layer 12 d 2. The capping layer 12 c may serve to protect the gate electrode 12 e 2. The capping layer 12 c may have a surface substantially coplanar with the top surface of the active region 10 a.

In some embodiments, the capping layer 12 c may include a dielectric material, such as silicon oxide (SiO₂), silicon nitride (Si₃N₄), silicon oxynitride (N₂OSi₂), and silicon nitride oxide (N₂OSi₂). In some embodiments, the capping layer 12 c may include a silicon nitride liner and a spin-on-dielectric (SOD) material.

The gate structure 11 may include dielectric layers 11 d 1, 11 d 2, gate electrodes 11 e 1, 11 e 2, and a capping layer 11 c. The gate structure 11 has a structure similar to the structure of the gate structure 12, except that the gate structure 11 is disposed in the isolation region 10 i.

Referring to FIG. 1C, the trench 10 t 2 extends through one of the active regions 10 a and the isolation region 10 i. The trench 10 t 2 may have a fin structure in which the active region 10 a protrudes more than the isolation region 10 i. In other words, a depth of the passing gate, which runs across the isolation region 10 i, is greater than a depth of the main gate, which runs across active region 10 a. Accordingly, the trench 10 t 2 for the gate structure 12 has different depths for a main gate region and a passing gate region.

The fin structure may increase the channel width and improve the electrical characteristics. In some embodiments, the fin structure may be omitted.

FIG. 2 is a schematic cross-sectional view of a semiconductor device 2 in accordance with some embodiments of the present disclosure. The semiconductor device 2 of FIG. 2 is similar to the semiconductor device 1 of FIG. 1 , except for the differences described below.

The gate structure 12 of the semiconductor device 2 further includes a barrier layer 12 b 1 disposed between the dielectric layer 12 d 1 and the gate electrode 12 e 1. The barrier layer 12 b 1 may be conformally formed on the surface of the dielectric layer 12 d 1. The base portion of the dielectric layer 12 d 2 may be disposed on the barrier layer 12 b 1. The base portion of the dielectric layer 12 d 2 may contact the barrier layer 12 b 1.

In some embodiments, the barrier layer 12 b 1 may include a metal-based material. The barrier layer 12 b 1 may include metal nitride. The barrier layer 12 b 1 may include titanium nitride (TiN) or tantalum nitride (TaN).

The gate structure 12 of the semiconductor device 2 further includes a barrier layer 12 b 2 disposed between the dielectric layer 12 d 2 and the gate electrode 12 e 2. The barrier layer 12 b 2 may be disposed on the base portion of the dielectric layer 12 d 2.

The distance t2 between the barrier layer 12 b 2 and the substrate 10 may be greater than the distance t1 between the barrier layer 12 b 1 and the substrate 10. For example, the barrier layer 12 b 2 and the barrier layer 12 b 1 may be spaced apart from the substrate 10 by different distances.

The barrier layers 12 b 1 and 12 b 2 may be formed of the same material or different materials. In some embodiments, the barrier layer 12 b 2 may include a metal-based material. The barrier layer 12 b 2 may include metal nitride. The barrier layer 12 b 2 may include titanium nitride (TiN) or tantalum nitride (TaN), tungsten nitride (WN) or combinations thereof.

FIG. 3 is a schematic cross-sectional view of a semiconductor device 3 in accordance with some embodiments of the present disclosure. The semiconductor device 3 of FIG. 3 is similar to the semiconductor device 1 of FIG. 1 , except for the differences described below.

The semiconductor device 3 may further include an isolation layer 30, contact plugs 31, 33, a bit-line structure 32, and a memory element 34.

The isolation layer 30 may be a single layer or a multi-layer. The isolation layer 30 may include silicon oxide (SiO₂), silicon nitride (Si₃N₄), silicon oxynitride (N₂OSi₂), silicon nitride oxide (N₂OSi₂), etc.

The isolation layer 30 may serve to isolate adjacent contact plugs 33 from each other.

The contact plug 31 may be electrically connected with the bit-line structure 32 and the first doped region 101. The bit-line structure 32 may include a bit-line 32 a, a bit line hard mask layer 32 b and a spacer 32 c. The bit-line 32 a may include at least one material selected among a polysilicon (poly-Si), a metal silicide, a metal nitride and a metal. The bit line hard mask layer 32 b may include a silicon oxide or a silicon nitride. The spacer 32 c may include a dielectric material.

The contact plug 33 may be electrically connected with the memory element 34 and the second doped region 102.

In some embodiments, the contact plugs 31 and 33 may include a suitable conductive material. For example, the contact plugs 31 and 33 may include tungsten (W), copper (Cu), aluminum (Al), silver (Ag), an alloy thereof, or a combination thereof.

The memory element 34 may be a capacitor. Accordingly, the memory element 34 may include a storage node which contacts the contact plug 33. The storage node may have a cylinder shape or a pillar shape. A capacitor dielectric layer may be formed on the surface of the storage node.

As the DRAM device becomes more highly integrated, it becomes more difficult to isolate a main gate (such as an electrode of the gate structure 12) in a memory cell from a passing gate (such as an electrode of the gate structure 11) in an adjacent memory cell. For example, when a passing gate is turned on, an inversion layer may be created that may extend the source/drain junction, creating an internal electric field. GIDL may be accelerated by the internal electric field.

By forming a thicker dielectric layer (i.e., the dielectric layers 12 d 1 and 12 d 2) between the upper electrode (i.e., the gate electrode 12 e 2) and the substrate, the effective electric field may be reduced and hence GIDL may be lowered. Therefore, interference between word-lines in different memory cells can be avoided, a data retention time can be extended, and the operational reliability of the semiconductor device can also be improved.

In addition, the lower gate electrode (i.e., the gate electrode 12 e 1) and the upper gate electrode (i.e., the gate electrode 12 e 1) can receive different voltages, which helps to mitigate GIDL while maintaining good device performance.

FIGS. 4A, 4B, 4C, 4D, 4E, 4F, 4G, 4H, 4I, 4J, 4K, 4L, 4M, 4N, and 4O illustrate stages of a method of manufacturing a semiconductor device in accordance with some embodiments of the present disclosure. At least some of these figures have been simplified for a better understanding of the aspects of the present disclosure. In some embodiments, the semiconductor device 3 in FIG. 3 may be manufactured by the operations described below with respect to FIGS. 4A, 4B, 4C, 4D, 4E, 4F, 4G, 4H, 4I, 4J, 4K, 4L, 4M, 4N, and 4O.

Referring to FIG. 4A, the substrate 10 may be provided. The sublayer 11 a may be disposed in the substrate 10. In some embodiments, the sublayer 11 a may be formed by trench etching followed by filling the trench with a dielectric material. In some embodiments, the sublayer 11 a may be formed by a chemical vapor deposition (CVD) process. In some embodiments, the sublayer 11 a may include a low-k dielectric material, such as fluorine-doped silicon dioxide (FSG), organosilicate glass (OSG), carbon-doped oxide (CDO), porous silicon dioxide, etc. In some embodiments, the sublayer 11 a may be a dielectric material having a dielectric constant that is lower than that of silicon dioxide (SiO₂), or a dielectric material having a dielectric constant lower than about 4.0.

As shown in FIG. 4A, the isolation region 10 i is formed in the substrate 10. The active region 10 a is defined by the isolation region 10 i. The isolation region 10 i may be formed through an STI (shallow trench isolation) process. For example, after a pad layer (not shown) is formed on the substrate 10, the pad layer and the substrate 10 are etched using an isolation mask (not shown) to define an isolation trench. The isolation trench is filled with a dielectric material, and accordingly, the isolation region 10 i is formed.

A wall oxide, a liner and a gap-fill dielectric may be sequentially formed as the isolation region 10 i. The liner may be formed by stacking silicon oxide (SiO₂) and silicon nitride (Si₃N₄). The gap-fill dielectric may include a SOD material. In another embodiment of the present invention, in the isolation region 10 i, a silicon nitride may be used as the gap-fill dielectric. The isolation trench may be filled with a dielectric material through a CVD process. Also, a planarization process such as chemical-mechanical polishing (CMP) may be additionally performed.

Referring to FIG. 4B, a plurality of trenches 10 t 1 and 10 t 2 may then be formed in the substrate 10. Each of the trenches 10 t 1 and 10 t 2 may have a line shape crossing the active region 10 a and the isolation region 10 i. Each of the trenches 10 t 1 and 10 t 2 may be formed by an etch process of the substrate 10 using a hard mask layer 40 as an etch mask. The hard mask layer 40 may be formed on the substrate 10, and have line-shaped openings. The hard mask layer 40 may be formed of a material having an etch selectivity to the substrate 10. Each of the trenches 10 t 1 and 10 t 2 may be formed to be shallower than the isolation trench. In some embodiments, the bottom edge of each of the trenches 10 t 1 and 10 t 2 may have a curvature.

The active region 10 a and the isolation region 10 i may be simultaneously etched to form the trenches 10 t 1 and 10 t 2. In some embodiments, the isolation region 10 i is more deeply etched than the active region 10 a due to an etch selectivity between the active region 10 a and the isolation region 10 i. Therefore, the gate trench may have a fin structure in which the active region 10 a protrudes further than the isolation region 10 i in the gate trench.

Referring to FIG. 4C, a dielectric layer d1 may be formed on the surface of each of the trenches 10 t 1 and 10 t 2. Before the dielectric layer d1 is formed, the inside surface of each of the trenches 10 t 1 and 10 t 2 that is damaged from the etch process may be recovered. For example, sacrificial oxide may be formed by a thermal oxidation treatment, and then the sacrificial oxide may be removed.

The dielectric layer d1 may be formed by a thermal oxidation process. In some embodiments, the dielectric layer d1 may be formed by a deposition process, such as a CVD process or an ALD process.

Referring to FIG. 4D, a barrier layer b1 may be formed on the dielectric layer d1 and the hard mask layer 40. The barrier layer b1 may be conformally formed on the surface of the dielectric layer d1. The barrier layer b1 may be formed by the ALD or CVD process.

Referring to FIG. 4E, a conductive layer e1 may be formed on the barrier layer b1. The conductive layer e1 may be formed on the barrier layer b1 to fill each of the trenches 10 t 1 and 10 t 2. The conductive layer e1 may include a low-resistance metal material. The first conductive layer 19A may include tungsten (W). The conductive layer e1 may be formed by the CVD or ALD process.

Referring to FIG. 4F, a recessing process may be performed. The recessing process may be performed by a dry etch process, for example, an etch-back process. The barrier layers 11 b 1 and 12 b 1 may be formed by performing the etch-back process on the barrier layer b1. The gate electrodes 11 e 1 and 12 e 1 may be formed by performing the etch-back process on the conductive layer e1.

The barrier layer 11 b 1 and the gate electrode 11 e 1 may be formed inside the trench 10 t 1. The top surfaces of the barrier layer 11 b 1 and the gate electrode 11 e 1 may be substantially coplanar or located at the same level. The barrier layer 12 b 1 and the gate electrode 12 e 1 may be formed inside the trench 10 t 2. The top surfaces of the barrier layer 12 b 1 and the gate electrode 12 e 1 may be substantially coplanar or located at the same level.

In some embodiments, a planarization process may be performed in advance to expose the top surface of the hard mask layer 40, and then the etch-back process may be performed.

After the barrier layer 12 b 1 and the gate electrode 12 e 1 are formed, a surface 12 d 1 s of the dielectric layer 12 d 1 may be partially exposed.

Referring to FIG. 4G, a dielectric layer d2 may be formed on the barrier layer 12 b 1 and the gate electrode 12 e 1. The dielectric layer d2 may directly contact the barrier layer 12 b 1 and the gate electrode 12 e 1. The dielectric layer d2 may directly contact the surface 12 d 1 s of the dielectric layer 12 d 1. The dielectric layer d2 may be formed by ALD or CVD.

Referring to FIG. 4H, a barrier layer b2 may be formed on the dielectric layer d2. The dielectric layer d2 may be disposed between the barrier layer b2 and the gate electrode 12 e 1. The barrier layer b2 may be non-conformally formed. The non-conformal barrier layer b2 may be formed by physical vapor deposition (PVD).

Referring to FIG. 4I, a part of the barrier layer b2 may be removed to expose a part of the dielectric layer d2. For example, an etch process may be performed on the barrier layer b2. Therefore, the barrier layer 11 b 1 and the barrier layer 11 b 2 may remain on the bottom surface of the dielectric layer d2.

Referring to FIG. 4J, a conductive layer e2 may be formed on the barrier layer 11 b 1, the barrier layer 11 b 2 and the dielectric layer 2. The conductive layer e2 may fill each trench. The conductive layer e2 may include a material having a low work function. The conductive layer e2 may include polysilicon having a low work function, for example, polysilicon doped with an N-type impurity. The conductive layer e2 may be formed by CVD or ALD.

Referring to FIG. 4K, a recessing process may be performed. The recessing process may be performed by a dry etch process, for example, an etch-back process. The gate electrodes 11 e 2 and 12 e 2 may be formed by performing the etch-back process on the conductive layer e2.

Referring to FIG. 4L, the capping layers 11 c and 12 c may be formed on the gate electrodes 11 e 2 and 12 e 2.

Referring to FIG. 4M, the capping layer 24 may be planarized and the hard mask layer 40 may be removed so that the top surface of the dielectric layers 12 d 1 and 12 d 2. Through a series of processes described above, buried gate structures 11, 12, 13 and 14 may be formed.

Referring to FIG. 4N, a doping process of an impurity is performed by implantation or other doping technique. Accordingly, the first doped region 101 and second doped region 102 are formed in the substrate 10.

In some embodiments, the first doped region 101 and second doped region 102 may be formed subsequent to other operations described. For example, the first doped region 101 and second doped region 102 may be formed subsequent to one of the operations in FIGS. 4A, 4B, 4C, 4D, 4E, 4F, 4G, 4H, 4I, 4J, 4K and 4L.

Referring to FIG. 4O, the isolation layer 30 may be formed on the top surface of the structure from FIG. 4N by, for example, ALD, CVD, PVD, remote plasma CVD (RPCVD), plasma enhanced CVD (PECVD), coating, etc. The isolation layer 30 may be patterned to define the locations of the contact plugs 31, 33 formed in the subsequent operations. The contact plug 31 may be disposed over the first doped region 101. The contact plug 33 may be disposed over the second doped region 102. Then, the bit-line structure 32 may be electrically connected with the contact plug 31. The memory element 34 may be electrically connected with the contact plug 33.

In some embodiments, subsequent to the formation of the memory element 34, a wiring layer (not shown in the figures) may be formed on the memory element 34. For example, the wiring layer may have a multilayer wiring structure which includes a plurality of wiring layers and interlayer insulating films.

FIG. 5 illustrates a flow chart of a method 50 of manufacturing a semiconductor device in accordance with some embodiments of the present disclosure.

In some embodiments, the method 50 may include a step S51 of forming a trench in a substrate. For example, as shown in FIG. 4B, the plurality of trenches 10 t 1 and 10 t 2 may be formed in the substrate 10.

In some embodiments, the method 50 may include a step S52 of disposing a first barrier layer in the trench. For example, as shown in FIG. 4D, the barrier layer b1 may be formed on the dielectric layer d1 and the hard mask layer 40. The barrier layer b1 may be disposed in the trenches 10 t 1 and 10 t 2.

In some embodiments, the method 50 may include a step S53 of disposing a lower gate electrode on the first barrier layer in the trench. For example, as shown in FIG. 4E, the conductive layer e1 may be formed on the barrier layer b1. For example, as shown in FIG. 4F, the gate electrodes 11 e 1 and 12 e 1 may be formed by performing the etch-back process on the conductive layer e1. In some embodiments, the barrier layers 11 b 1 and 12 b 1 may be formed by performing the etch-back process on the barrier layer b1.

In some embodiments, the method 50 may include a step S54 of disposing a dielectric layer on the lower gate electrode in the trench. For example, as shown in FIG. 4G, the dielectric layer d2 may be formed on the barrier layer 12 b 1 and the gate electrode 12 e 1. Similarly, the dielectric layer d2 may be formed on the barrier layer 11 b 1 and the gate electrode 11 e 1.

In some embodiments, the method 50 may include a step S55 of disposing a second barrier layer on the dielectric layer in the trench. For example, as shown in FIG. 4H, the barrier layer b2 may be formed on the dielectric layer d2. For example, as shown in FIG. 4I, the barrier layer 11 b 1 and the barrier layer 11 b 2 may remain on the bottom surface of the dielectric layer d2.

In some embodiments, the method 50 may include a step S56 of disposing an upper gate electrode on the dielectric layer in the trench. For example, as shown in FIG. 4J, the conductive layer e2 may be formed on the barrier layer 11 b 1, the barrier layer 11 b 2 and the dielectric layer 2. For example, as shown in FIG. 4K, the gate electrodes 11 e 2 and 12 e 2 may be formed by performing the etch-back process on the conductive layer e2.

One aspect of the present disclosure provides a semiconductor device. The semiconductor device includes a substrate having a trench and a gate structure in the trench. The gate structure includes a lower gate electrode, an upper gate electrode over the lower gate electrode and a first dielectric layer partially disposed between the lower gate electrode and the upper gate electrode.

Another aspect of the present disclosure provides a semiconductor device. The semiconductor device includes a substrate having a trench and a gate structure in the trench. The gate structure includes a lower gate electrode and an upper gate electrode over the lower gate electrode. The lower gate electrode and the upper gate electrode are configured to receive different voltages.

Another aspect of the present disclosure provides a method of manufacturing a semiconductor device. The method includes forming a trench in a substrate, disposing a lower gate electrode in the trench, and disposing a first dielectric layer on the lower gate electrode. The method also includes disposing an upper gate electrode on the first dielectric layer.

By forming a thicker dielectric layer between the upper electrode and the substrate, the effective electric field may be reduced and hence Gate Induced Drain Leakage (GIDL) may be lowered. Therefore, interference between word-lines in different memory cells can be avoid. A data retention time can be extended, and the operational reliability of the semiconductor device can also be improved.

In addition, the lower gate electrode and the upper gate electrode can receive different voltages, which helps to mitigate GIDL while maintaining good device performance.

Although the present disclosure and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the disclosure as defined by the appended claims. For example, many of the processes discussed above can be implemented in different methodologies and replaced by other processes, or a combination thereof.

Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, and composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the present disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present disclosure. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps. 

What is claimed is:
 1. A semiconductor device, comprising: a substrate having a trench; and a gate structure in the trench, wherein the gate structure comprising: a lower gate electrode; an upper gate electrode over the lower gate electrode; and a first dielectric layer partially disposed between the lower gate electrode and the upper gate electrode.
 2. The semiconductor device of claim 1, wherein the lower gate electrode and the upper gate electrode are configured to receive different voltages.
 3. The semiconductor device of claim 2, wherein a voltage of the lower gate electrode is greater than a voltage of the upper gate electrode.
 4. The semiconductor device of claim 2, wherein a voltage difference between the lower gate electrode and the upper gate electrode is greater than 0.3 volts (V).
 5. The semiconductor device of claim 1, further comprising: a second dielectric layer partially disposed between the lower gate electrode and the substrate; wherein the first dielectric layer is spaced apart from the substrate by the second dielectric layer; and the first dielectric layer and the second dielectric layer comprises different densities.
 6. The semiconductor device of claim 1, wherein the first dielectric layer directly contacts the lower gate electrode and the upper gate electrode.
 7. The semiconductor device of claim 1, wherein the gate structure is disposed in an active region of the substrate.
 8. The semiconductor device of claim 1, wherein the gate structure is disposed in an isolation region of the substrate.
 9. The semiconductor device of claim 1, further comprising: a first barrier layer disposed between the lower gate electrode and the substrate; wherein the first barrier layer contacts the first dielectric layer.
 10. The semiconductor device of claim 1, further comprising: a second barrier layer disposed between the upper gate electrode and the first dielectric layer.
 11. A semiconductor device, comprising: a substrate having a trench; and a gate structure in the trench, wherein the gate structure comprising: a lower gate electrode; and an upper gate electrode over the lower gate electrode; wherein the lower gate electrode and the upper gate electrode are configured to receive different voltages.
 12. The semiconductor device of claim 11, wherein the lower gate electrode and the upper gate electrode are spaced apart from the substrate by different distances.
 13. The semiconductor device of claim 11, wherein a voltage of the lower gate electrode is greater than a voltage of the upper gate electrode.
 14. The semiconductor device of claim 11, wherein a voltage difference between the lower gate electrode and the upper gate electrode is greater than 0.3 volts (V).
 15. The semiconductor device of claim 11, further comprising: a first dielectric layer partially disposed between the lower gate electrode and the substrate.
 16. The semiconductor device of claim 15, wherein the first dielectric layer is spaced apart from the upper gate electrode by a second dielectric layer, the first dielectric layer and the second dielectric layer comprises different densities, and the second dielectric layer directly contacts the lower gate electrode and the upper gate electrode.
 17. The semiconductor device of claim 11, wherein the gate structure is disposed in an active region of the substrate.
 18. The semiconductor device of claim 11, wherein the gate structure is disposed in an isolation region of the substrate.
 19. The semiconductor device of claim 11, further comprising: a first barrier layer disposed between the lower gate electrode and the substrate; and a second barrier layer disposed between the upper gate electrode and the lower gate electrode; wherein the first barrier layer and the second barrier layer are spaced apart from the substrate by different distances.
 20. A method of manufacturing a semiconductor device, comprising: forming a trench in a substrate; disposing a lower gate electrode in the trench; disposing a first dielectric layer on the lower gate electrode; and disposing an upper gate electrode on the first dielectric layer. 